Type 1 diabetes is an organ-specific autoimmune disease that requires life-long monitoring and treatment to prevent damage of multiple organs. The research proposed herein aims to characterize protective commensal bacteria influencing the pathogenesis of type 1 diabetes in a prototypical murine model, the non-obese diabetic (NOD) mouse. The hypothesis is based on the fact that the incidence of type 1 diabetes is markedly lower in male than female NOD mice under specific-pathogen-free (SPF) conditions that allow colonization with commensals. However, the absence of microbiota under germ-free conditions leads to 100% penetrance of the phenotype in both genders. It is hypothesized that gut microbiota mediate this sex bias by influencing the spontaneous autoimmune response. We therefore plan to analyze potential candidate microbiota as well as the microbiome in male, female and sex-hormone-ablated mice. We will also dissect the immunological differences between both genders, with a focus on T cell subsets, given their importance in the pathogenesis of this disease. Finally, we plan to study the influence of oral gavage with candidate microbiota and antibiotic treatments on disease development and T cell function. We specifically plan to achieve these goals as follows: Specific Aim 1: To examine candidate microbiota and the unbiased microbiome in male, female and sex-hormone-ablated NOD mice. We will perform next-generation pyrosequencing of each gastrointestinal segment from NOD mice. We will analyze the microbiome and selected candidate microbiota for possible gender differences in young adult NOD mice and at multiple time points from weaning age until development of disease. Specific Aim 2: To analysis the T cell compartment in the small intestine and colon of male versus female NOD mice. We will analyze various T cell subsets using flow cytometry and RNA microarray profiling to identify functional differences between male and female gastrointestinal immune compartments. Specific Aim 3: To gavage SPF-housed female and germ-free male NOD mice with potentially protective microbiota that have been identified in Specific Aim 1, and to perturb the host with selective antibiotic combinations. We will also investigate any alterations in T cell functions induced by these manipulations. We anticipate that the proposed research will lead to discovery of new mechanisms in the pathogenesis of type 1 diabetes, and opens the novel avenue of gender-associated microbiota in autoimmunity in general. The research is expected to have broad implications for sex-biased autoimmune diseases with the potential for development of new treatment strategies. The project deals with the influence of gender-associated commensal gut bacteria on type 1 diabetes in the non-obese diabetic (NOD) mouse strain. We plan to identify beneficial gut bacteria that protect male NOD mice under standard housing conditions and characterize their impact on disease in highly susceptible germ-free NOD mice. Exploration of the commensals'effects on the immune system and sex bias in this mouse model will help to better understand the female preponderance of human autoimmune diseases in general, and open possibly new treatment strategies.